1. Field of the Invention
The present invention relates to a capacitor structure and a fabrication method thereof, and more particularly, to a dynamic random access memory stack capacitor structure having a particular supporting structure and a fabrication method thereof.
2. Description of the Prior Art
A dynamic random access memory (DRAM) device is made up of many memory cells. Generally, the memory cell is a semiconductor memory device with an access transistor and a storage capacitor. Each memory cell can store one bit of data by storing electric charges in the storage capacitor.
In general, the storage capacitor contains an upper electrode, a dielectric layer, and a lower electrode. The storage capability of the storage capacitor is proportional to an overlapping area between the upper/lower electrodes and the dielectric layer. Since modern electrical products are developed with minimized sizes thereof, the area of each memory cell tends to be reduced, so that the DRAM device can be designed with high integrated density. However, the reduction of the area of each memory cell leads to lower storage capability of the memory cell, which requires high refresh frequency and therefore affects the performance of the DRAM device. Currently, two methods are provided to increase storage capability of the storage capacitor. A method is proposed to use a material with higher dielectric constant for the dielectric layer, and the other method is proposed to increase the overlapping area between the upper/lower electrodes and the dielectric layer.
Several methods of increasing the area of the capacitor electrode have been proposed in the prior art. For example, crown-type stacked capacitors can be used to increase the total surface area of the capacitor electrode owing to its sidewall structures. According to the prior art, lithography and etching process is performed to form a plurality of crown-type stacked capacitors, and each crown-type stacked capacitor is supported by a supporting structure. However, the existing supporting structures are only formed at a top of each crown-type stacked capacitor and tend to be damaged, which may cause a reduction of product yield. Therefore, a capacitor structure having a particular supporting structure and a fabrication method thereof are required.